1. Field of the Invention
The present invention relates to variable tread vehicles in which spacing between a pair of wheels is adjustable.
2. Description of the Prior Art
With various types of farm and construction vehicles, it is desirable to be able to change the spacing between wheels or threads in order to accommodate different working conditions. This is particularly true in the case of farm vehicles, which often must be used in conjunction with different types of crops having different row spacing. One type of agricultural vehicle which provides an adjustment of wheel tread is the John Deere 6000 Hi-Cycle sprayer. This vehicle has a pair of rear wheels which are driven by chain drives through a pair of drop axle assemblies. The wheel tread (or spacing) of the 6000 Hi-Cycle sprayer is adjustable by jacking up one side of the vehicle, removing several bolts which attach the drop axle to a pair of rails, and prying the drop axle inward or outward using a pry bar which extends through a hole in the deck and through a tab in the top of the drop axle housing. Once the selected new position of the drop axle has been attained, the bolts must be reinserted and tightened. The same procedure is then repeated with the opposite drop axle assembly.
This type of manual adjustment of wheel tread is inconvenient, and requires several hours of time. This results in lost production time of both the operator and the vehicle each time a field having a different row spacing is to be sprayed.
In the past, various types of tractors and other farm vehicles, as well as construction vehicles, have been proposed which have some form of mechanically adjustable tread. For example, in the Beatty U.S. Pat. No. 1,811,661, a rack-and-pinion type of arrangement is used to change tread.
In the Brown U.S. Pat. No. 1,967,283, a tractor is shown which has oppositedly threaded shafts. An axle housing has internally threaded portions which engage the threaded shafts. Adjustment of the spacing between the wheels can be achieved by driving the tractor either forwardly or backwardly.
The Brown et al U.S. Pat. No. 2,002,002 shows a rack-and-pinion arrangement for changing wheel tread.
The Johnson U.S. Pat. No. 2,173,419 changes tread through a gear which drives left and righthand treaded end portions into treaded bores of a pair of slide blocks. The slide blocks slide within a barrel and have wheel spindles attached at their ends.
The Hamilton U.S. Pat. No. 2,228,454 shows a telescoping type of arrangement in which the spacing of opposite sides of the tractor, and thus the tractor tread, can be adjusted.
The kondracki U.S. Pat. No. 2,681,231 shows a trench digger having an adjustable tread. Adjustment of the tread is achieved by removing fastening screws from the ends of the axle section and either a hydraulic mechanism is used to separate the tread, or a threaded shaft is used.
The Jackson U.S. Pat. No. 2,885,018 uses a threaded shaft to adjust the tread of a tractor.
The Jamme U.S. Pat. No. 3,306,390 shows a vehicle in which the wheels are supported on pivotable arms. The position of the four arms of the vehicle are controlled by hydraulic cylinders.
The Hansen U.S. Pat. No. 3,589,744 shows a telescoping type of arrangement for adjusting the tread of the wheels of a three-wheeled farm vehicle.
There is a continuing need, however, for improved adjustable wheel tread vehicles which provide rapid and simple change of wheel tread without requiring a large number of components which increase the cost of the vehicle significantly and reduce its reliability.